A magnetron rotating cathode sputtering apparatus a magnetic filed generation device inside a cylindrical target, and performs sputtering by rotating a target while cooling from the inside of the target. The entire face of the target material becomes an erosion state, and is uniformly cut. As a result, markedly high target use efficiency (60% or higher) is obtained, compared with use efficiency (20-30%) of the conventional flat plate type magnetron rotating cathode sputtering apparatus. Further, by rotating a target, large power per unit area can be introduced, compared with the conventional flat plate type magnetron rotating cathode sputtering apparatus. As a result, high film formation rate is obtained (see, for example, JP-T-58-500174) (The term “JP-T” as used herein means a published Japanese translation of a PCT patent application). Such a rotating cathode sputtering method is wide spread in a metal target which is easily processed into a cylindrical shape and has high mechanical strength. However, in a ceramic target having low strength and being brittle, cracks, deformation or the like are liable to occur during its production. For this reason, only a target produced using a specific material or produced by a specific process has been used.
It is known that the conventional flat plate type the conventional flat plate type sputtering target improves its quality by increasing a density of its ceramic sintered body. For example, in ITO (Indium Tin Oxide) used as a transparent conductive film, there are a method of obtaining a high density target by sintering the ITO in a pressurized oxygen atmosphere (for example, JP-A-3-060351), and a method in which density of a sintered body is increased and diameter of sintered particles is controlled, thereby a sputtering rate increases, and generation of nodule on a target surface, causing fine particles, is effectively prevented (for example, JP-A-5-311428). Thus, various ingenuities have been made in the flat plate type ITO target. In particular, in view of that a high density target produced by a sintering method has excellent quality, the sintering method is recently employed as a production method of the flat plate type target.
However, when density of a cylindrical ceramic target is made to have high density using the sintering method, there was the problem that sintering shrinkage is large, so that cracks, deformation and the like occur in sintering. For this reason, the cylindrical target that can be produced by the sintering method has low sintering shrinkage and low density showing a relative density of about 80%, as described in, for example, working examples of JP-A-3-153868 or comparative examples of JP-A-6-156431.
Proposed methods other than the sintering method include a method of forming a target layer on an outer surface of a cylindrical substrate by a plasma spray method (for example, JP-A-10-068072), and a method of forming a target by charging a powder on an outer surface of a cylindrical substrate, and performing hot isotropic pressing (HIP) (for example, JP-A-05-156431). Those methods directly produce a target on the cylindrical substrate. Therefore, the cylindrical substrate and target material (sintered body) cannot be separated from the used target. This gives rise to the problems that reuse of a substrate or recycle of a target material, generally performed, is impossible or difficult, and such is not economical in a sputtering target using an expensive material.
In a method of forming a target layer by an arc spray method, the layer formed tends to contain air bubbles, and have low density. In ITO target described in JP-A-10-068072, the maximum density is 5.3 g/cm3, and this density merely corresponds to a relative density 74% (calculated from true density of ITO: 7.156 g/cm3). This is very low density, compared with a high density target recently used. A method of forming a target by HIP requires large cost, which is not economical. Further, where a sputtering target is produced using ceramics sintered in a reducing atmosphere as in HIP, problems arise that oxides, particularly, ITO, have decreased oxygen content, and quality of a film obtained by sputtering deteriorates.
Where a target is produced by a sintering method, a sintered body must be bonded to a cylindrical substrate. However, this involves the problem that cracks or breakage are liable to occur in such a bonding step. In the cylindrical target, a method of preventing generation of cracks or breakage in a bonding step has been proposed by that instead of using, as a substrate, Cu which has conventionally been used in a flat plate type target, for example, Ti having a coefficient of thermal expansion very similar to that of ITO sintered body being a target material is used as a cylindrical substrate (for example, JP-A-06-293963 and JP-A-08-060351). However, considering that Ti is an expensive material, and Ti can be applied to only the case that the target material and the substrate have the similar coefficient of thermal expansion, use of a cylindrical substrate made of Ti was not yet sufficient in a production process of the cylindrical ceramic target. In this method, heating temperature in bonding is low, and this is effective as a countermeasure for breakage in a bonding step. However, Ag paste is very hard after curing, and does not have ductility as possessed by indium solder. Consequently, the target does not act as a buffering material when the target is heated and expanded in sputtering, and there has been the possibility that the target cracks during sputtering.